1. Field of the Invention
This invention relates to a process and an apparatus for producing anhydrous ethanol. More particularly it relates to a process and an apparatus wherein an absorption heat pump and a mechanical heat pump are included in a process and an apparatus for producing anhydrous ethanol from dilute ethanol using a concentration column, an azeotropic distillation column and a solvent recovery column.
2. Description of the Prior Art
As for processes and apparatus for obtaining anhydrous ethanol from dilute ethanol by concentration through distillation, those consisting of a combination of a concentration column, an azeotropic distillation column and a solvent recovery column have generally been conventionally employed, and steam has often been used as the heat source therefor. In order to save the steam, i.e. as an energy saving feature, if the steam at the top of the distillation column is compressed and pressure-elevated by means of a compressor, the steam temperature at the top is considerably higher than the temperature in the case of condensation at atmospheric pressure. A process of heating the boiler liquid of the column by the compressed steam has been known.
However, when an electric motor is used as the machine for driving such a compressor, a considerably high amount of electric power is consumed for driving the compressor. Thus, the use of such a compressor is impractical in districts where electric power is not available or in districts where electric power is supplied at a high cost.
On the other hand, in such districts, if dilute ethanol which has been obtained from agricultural materials according to a fermentation process is used as the raw material, a large amount of steam is obtained by operating a boiler using as fuel therefor residue from the agricultural products such as bagasse.
When utilizing such steam as the power source of the compressor, it may be considered to employ a steam turbine as the machine for driving the compressor. However, in the case where the turbine is a condensation turbine, a large part of the heat quantity of steam used is transferred to cooling water in the condenser; hence such a process is uneconomical.
The present inventors have made strenuous studies on effective utilization of waste heat in the case where a steam turbine is employed, and as a result, have found that the waste heat can be utilized as the heat source for an absorption heat pump and as the heat source for the reboiler of a solvent recovery column. With respect to the absorption heat pump, if the heat quantity of the vapor at the top of a concentration column or an azeotropic distillation column is utilized for heating the boiler liquid of the respective columns, then the heat source for the absorption heat pump itself is not required; hence the heat quantity of the steam used for the steam turbine can be effectively utilized to a large extent in accordance with the present invention.
As is apparent from the foregoing, an object of the present invention is to provide a process and an apparatus for employing a heat pump in order to effectively utilize the heat quantity of steam at the top of an apparatus for producing anhydrous alcohol, and to provide a process and apparatus for producing anhydrous alcohol wherein a steam turbine is employed whereby the heat quantity of the steam used for the turbine can be effectively utilized. Other objects will be apparent from the following description.